Early
settlers turned the prairie into cropland, and used its
sod to build homes

When
Europeans first reached North America, prairie land covered
more than a quarter of the continental US, stretching thousands
of miles from Canada to Mexico, and from east of the Mississippi
to the Rockies. A complex system of interdependent plants
and animals, the prairie once supported some 60 million bison.
By 1900, the American westward expansion had virtually wiped
out the bison, the prairie and the Plains Indians who once
lived there.

In "Prairie Comeback," Alan Alda visits the Nature
Conservancy's Tallgrass Prairie Preserve in northeast Oklahoma,
where director Harvey Payne
and chief scientist Bob
Hamilton are seeking to restore the full prairie ecosystem
on a 50-square-mile former cattle ranch. They begin with two
key ingredients - bison and fire.

Broadleaf
plants add to the prairie's overall biodiversity by producing
flowers and seeds

Prairie
plants are specially adapted to fire. Their deep root systems
help them survive and are even stimulated by a blaze. Bison
like to graze on the young tender shoots of grasses that sprout
in the aftermath of a burn. This basic interaction is the
foundation of the prairie ecosystem. The broadleaf, flowering
plants ignored by the bison grow back in force, since they
have less competition from grasses. Such plants attract an
array of birds, insects and small mammals -- until, after
a couple of years, the grasses recover, and the whole process
begins again.

With
carefully timed and rotating burns, the Natute Conservancy
hopes to restore the quintessential American ecosystem to
at least this small corner of the Plains.